Combined effects of the earthworm casts application and fallow time on runoff and sediment loss by raindrop splashing in the Loess Plateau, China.

The importing of sources of exogenous organic carbon is an effective method for the prevention of soil degradation in sloping soils. Earthworm casts (ECs) have been recognised as a contributor to long-term carbon protection, but relatively few studies have examined the temporal impact ECs have on the achievement of this goal and its efficacy in the mitigation of soil erosion challenges in the Loess Plateau region in China. This study conducted field simulated rainfall experiments as a means of investigating the effects of five ECs (0, 200, 400, 600 and 800 g/m, labelled CG, E1, E2, E3 and E4) on runoff, sediment and soil aggregate composition after 60, 90 and 150 days of fallow. As E4 was fallow for 150 days, the total runoff, runoff coefficient and total sediment amount decreased by 34.0%, 37.6% and 82.80% in comparison to CG. The runoff and sediment analytical models were able to accurately simulate the runoff and sediment yield processes through ECs application (R≥0.704, RMSE≤1.108, NSE≥0.513). After being fallow for 150 days, soil sorptivity (S) increased from 0.151 cm/min to 0.310 cm/min as ECs application quantity increased. In contrast, the calibration constants of splash erosion (C) decreased from 0.150 to 0.090 and runoff erosion (C) decreased from 0.120 to 0.081. ECs were found to considerably enhance the number of aggregates that were more prominent than 0.25 mm in size. When E4 was fallow for 150 days, the fraction of >0.25 mm aggregate (WSA) increased by 120.69% in comparison to CG. The mean weight diameter (MWD) grew by 105.96%, the geometric mean diameter (GMD) increased by 98.81% and the soil erodibility value K improved by 43.78%. When the amount of ECs was 800 g/m, the stability of soil aggregates was effectively improved against water erosion while runoff and sediment transport were controlled. This can help improve the current soil and water loss situation in the Loess Plateau while also improving cultivated land soil quality. At the same time, a longer fallow period time promotes soil aggregate formation. This study is focused on the exceptional performance of ECs in limiting soil erosion on the Loess Plateau in China, which may provide novel solutions for soil and water conservation and the prevention of non-point source pollution.